Forgeable high temperature cast alloys



United States Patent 3,177,076 FORGEABLE HIGH TEMPERATURE CAST ALLOYS George A. Timmons, Ferndale, and Marion Semchyshen, Dearborn, Mich, assignors to American Metal Climax, Inc., New York, N.Y., a corporation of New York No Drawing. Filed June 12, 196'1,'Ser. No. 116,251

8 Claims. (Cl. 75-176) This application is a continuation-in-part of application Serial No. 30,773, filed May 23, 1960, and now abandoned.

The present invention relates to molybdenum and/or tungsten base alloy castings which are capable of being worked at elevated temperatures and methods of making same.

In the past, the preferred method of making forgeable castings of molybdenum and tungsten has involved the addition of small quantities of carbon and the melting of the material in vacuum. For some purposes, carbon additions may be undesirable and the present invention resides in the discovery that boron may be substituted for carbon with similar results. Moreover, while vacuum melting is preferred, it is not essential when boron is used in lieu of carbon. Finally, it has been found that alloys containing more than 50%- tungsten are more easily worked and provide larger percentages of sound stock recovery on working than similar alloys containing carbon in lieu of boron.

The alloy castings of the present invention comprise alloys consisting primarily of molybdenum or tungsten or combinations of the two in any desired proportions. In accordance with the present invention, the castings are made by melting powders, chips or particles of the metals in combination with small quantities of boron in vacuum or an inert atmosphere such as argon. 1

The preferred method involves melting the metal in a vacuum preferably at an absolute pressure less than 100 microns of mercury. The boron is believed to combine with any oxygen present in the metal to form B which is gaseous at the melting temperatures. Therefore, it is extracted from the melting and melted material at a higher rate in a vacuum than would be the case if an inert atmosphere at a higher absolute pressure were employed. One of the most effective methods of achieving such a melting operation is in a consumable electrode arc furnace, one such furnace suitable for the purpose being disclosed in United States Patent 2,656,743. When this type of equipment is used the electrode is formed by sintering the powder or chips of metal constituting the charge. Another method which may be employed is to melt the material by an electron beam in a very high vacuum. In either case the molten material is collected in a watercooled copper mold.

The molybdenum or tungsten powder, chips or particles should contain as little oxygen as possible and preferably include not more than .05% oxygen, including oxygen which is both combinedand adsorbed. Sufficient boron is added to combine with all of the combined oxygen and leave some residual excess in the final product. For this purpose, the final product should contain from 005% to 50% boron and preferably not more than .OOS% oxygen.

It is known that the properties of molybdenum and tungsten castings may be improved by the addition of small quantities of other transition elements, and there fore the present invention is applicable also to molybdenum or tungsten alloys which contain such additions. Thus, the alloys of the present invention may contain "ice minor quantities of. one or more of the elements titanium, zirconium, tantalum, vanadium, columbium, chromium, iron, cobalt, nickel and hafnium- However, these elements increase the hardness of the alloy and therefore may be used, but in amounts not exceeding the following percentages if the alloy is to be worked;

' The eifectof all of the above listed elements on hot hardness is additive and, therefore, when two are present the maximum quantity of one is preferably reduced from the maximum given in theabove list in proportion to the extent that the other approaches its maximum. Still further reductions on the same "basis are preferably made if more than two are present. In all cases, less than the maximum values thus determined is preferred where it is important to achieve a high percentage of recovery of sound stock on working.

In the absence of carbon, at minimum residual quantity of about .005% boron is required to obtain a workable alloy. For this purpose, it should be noted that at the level of 005% boron, the methods of analysis employed by applicants are subject to a possible error of plus or minus .002%, and therefore the useful minimum may be as low as .003% boron. Larger quantities in the range of .O2% to .50% have a significant grain-refining effect and maybe employed for that purpose, if desired. When hafnium, zirconium or titanium are present, maximum strength is obtained if the residual boron is about onetenth by weight of the total of those three elements present and therefore where strength is a major consideration the quantity of residual boron may be increased to that value. If no hafnium, zirconium or titanium is present it is preferred to keep the boron content below .05% because the advantage of grain refinement obtained with larger quantities is for most purposes offset by an increase in the brittle to ductile transition temperature.

A particularly valuable class of alloys coming within the scope of the present invention is tungsten base alloys containing boron within the limits stated and from about 2 /2% to 35% molybdenum. These are particularly useful for applications in which an alloy is required which will evidence great strength at temperatures in the range of 2400 F. to 4000 F. As compared with similar alloys prepared'with carbon in place of boron, this class of alloys is more readily worked. This class of tungsten base, molybdenum-containing alloys has finer grain, greater strength and hardness at 2400 F. than tungstenboron alloys of the present invention which contain no molybdenum but are otherwise similar, and when the molybdenum content exceeds about 10%, they are easier to machine and have higher recrystallization temperatures. The hardness and strength of this class of alloys at elevated temperatures may be further increased by one or more of the elements hafnium, zirconium, tantalum and Columbium.

In the case of alloys containing about 65% or more tungsten, it is preferred to keep the boron content in the 7 range of .005 to .015 except where hafnium or zirconium are present in which event the boron may be increased up to about one-tenth by weight of the total of those two elements. Larger quantities of, boron may be employed but they increase the brittle toductile transition temperature which may be objectionable for-{some purposes. While grain refinement is obtained with larger quantities of boron, it is usually preferable to employ molybdenum for grain refinement Where the tungsten content exceeds65%.

Therefore, special advantages atvery high tempera. tures are achieved with a class of alloys ranging from 2 /2 to 35 molybdenurn, about .004%to .05% boron,

and the balance consisting essentially of tungsten. If

desired and to increase hightemperature strength, there may be added one or more elements from the group con sisting of hafnium, zirconium, tantalum and columbiurn, in which event theamount of boronmay be increased to a value. as high as one-tenth the total weight of hafnium and zirconiunr. For this purpose, the amount of each of the elements in the above group'may'range up to the maximum quantities given in the foregoing table, but

The hightensile strength 'of representative examples of the above alloys at 2400 F. may be seen from the following table:;. 1

Tensile Strength, Lbs/Sq. In. 7 Example V V 1 Stress Relieved, Recrystallized The advantage which results from increasingthe boron content when titanium is present is indicated by the fact that the alloys of Examples 3, 4 and, 5 had the following short-time tensile strength in ,pounds per square inch at Where ease, of Working is, important, it is preferred that the, amounts fall within the range of .10% to 2% haf nium, .Ol% to 50% zirconium, .10% to 1.50%"tantalurn,

and .10% to 2% 'columbiurn. d 7

Another class of alloys having excellent high temperature strength characteristics, but at slightly lower temperatures thanthe first class,qare those containing fiorn:

zero to 35% tungsten, '.004% to'.50% boron, and the balance consisting essentially of molybdenum. In this class, .the boron in excess'of about 02% performs a de-.

sirable grain-refining function. If desired, and to increase high temperature strength, there may be added to this second classof alloys one ormore elements from the group consisting of titanium zirconium, tantalum, 'vanadi-t I um, columbium, chromium, iron, cobalt, nickel and haf nium in amounts not exceeding those given in the force going table. If hafnium, ;'titanium or zirconium are present, maximum strength is obtained if the quantity of boron is increased up to about one-tenth by Weight of the total of those three elements present. To facilitate work ing, the preferred alloying elements from the last men-- tioned group and the maximum permissible quantity of each are: hafnium from 10% to 2%; titanium from .,15% to 3%; zirconium from .Ol% to tantalum from .10% to 2%; and columbium from .10% to 2%.

1600* F. in a fully recrystallized condition.

Example: Tensile strength This shows that as the boron contentapproaches about one-tenth the titanium content, the high temperature strength increases. In a stress relieved condition, these wise be required to obtain a workable alloy, it willbe appreciated that traces of carbon in the order of .005 or less are often found in these metals and that such quantities -may be present without deleterious effects; While it is preferred that the alloys of the present invention contain less than .Ol% carbon, larger quantities may be present without loss of-some .of the advantages of the invention, and this is particularly so in the case of alloys, 'containing'hafnium, zirconium or titanium.

Alloys made in accordance with the foregoing may be Worked by extrusion, hammering and rolling The critical stage in working is the initial breakdown which is Examples of alloys coming within the scope of the present invention include the following:

Ex- Molyb- V Tungsten, B0ron,- Carbon, Other ample denum, percent percent percent. Elements, N 0. percent percent preferably done by extrusion at .temperaturse in the, range or 23009 F. to 3400 F. At the higher temperatures, alloy steel extrusion dies lined with aluminum oxide or zirconium oxide have proven useful. Afterinitial breakdown, further working to bars, rods or sheets presents less dithculty.

What is claimed is: I I I 1. A. cast alloy characterized. by its capacity to be worked at elevated temperatures, said alloy castingcontaining from .005 to 50% boron,'at least one metal from the group consisting of titanium up to 14%, zirconium up to 2% tantalum-up to 9%,: columbium up to 10% and hafnium up to 12%, and thebalance consisting essentially of metal-from the group consisting ofmolybdenum and tungsten and mixtures'thereof. d

2. A cast alloy characterizedby its capacity ,to be worked at elevated temperatures, said alloy casting con-, taining frorn$005 to 50% -boron,1at leastone metal from the group consisting of titanium up to 14%, zirconium up to 2%, tantalum up to 9%, columbium up to 10%, and hafnium up to 12%, and the balance consistin'g, essentially ofmolybdenurn; 7

i 3. A.-cast alloycharacterized by its capacity to be worked at elevated temperatures, said alloy casting containing at least. one metal'trorn; the "group consisting of titaniumup tol4%, zirconium up to 2%, tantalum up to 9%, hafnium up, to 12%, 'columbiurnup to, 10%, saidv casting also includingfb'oron within'the range from about 7 005% to the larger of the values .50% and about onetenth of the total quantity of titanium, zirconium and hafnium present, and the balance consisting essentially of at least one metal from the group consisting of molybdenum and tungsten.

4. A cast alloy characterized by its capacity to be worked at elevated temperatures, said alloy containing from 2 /z% to 35% molybdenum, about 005% to .05% boron, and the balance consisting essentially of tungsten.

5. A cast alloy characterized by its capacity to be worked at elevated temperatures, said alloy containing from 2 /2 to 35% molybdenum, at least one metal from the group consisting of hafnium up to 12%, titanium up to 14%, zirconium up to 2%, tantalum up to 9%, columbium up to said casting also containing boron in an amount between about .005 and the larger of the values 50% and one-tenth of the total quantity of titanium, hafnium and zirconium present, and the balance consisting essentially of tungsten.

6. A cast alloy characterized by its capacity to be worked at elevated temperatures, said alloy containing from 2 /2% to 35 molybdenum, at least one metal from the group consisting of hafnium from .10% to 2%, titanium from .15 to 3%, zirconium from .O1% to 50%, tantalum from .10% to 1.50%, columbium from .10% to 2%, said casting also containing boron in an amount between about 005% and the larger of the values .05% and one-tenth of the total quantity of titanium, hafnium and zirconium present, and the balance consisting essentially of tungsten.

7. A cast alloy characterized by its capacity to be Worked at'elevated temperatures, said alloy containing at least one metal from the group consisting of hafnium from .10% to 2%, titanium from .15 to 3%, zirconium from .01% to .50%, tantalum from .10% to 2%, columbium from .10% to 2%, said casting also containing boron in an amount between about .005 and the larger of the values 50% and one-tenth of thetotal quantity of hafnium, titanium and zirconium present, and the halance of said casting consisting essentially of molybdenum.

8. A cast alloy characterized by its capacity to be worked at elevated temperatures, said alloy containing at least one metal from the group consisting of hafnium from .10% to 2%, titanium from .15% to 3%, zirconium from 01% to tantalum from .10% to 2%, columbium from .10% to 2%, said casting also containing boron in an amount between about .005 and the larger of the values .50% and one-tenth of the total quantity of hafnium, titanium and zirconium present, and the balance of said casting consisting of molybdenum and tungsten with the tungsten content not exceeding 35 References Cited by the Examiner UNITED STATES PATENTS 1,774,849 9/30 Schroter -176 2,163,354 6/39 Schmidt et al. 75-176 2,188,405 1/40 Hensel et al. 75-176 2,234,969 3/41 Hensel et a1 75-176 X 2,253,533 8/41 Ruben 75-176 X 2,580,273 12/51 Bens et al 75-176 2,678,269 5/54 Ham et al. 75-176 FOREIGN PATENTS 408,662 4/34 Great Britain. 584,289 1/ 47 Great Britain.

OTHER REFERENCES Institute of Metals, Journal, vol. 82, Bulletin No. 2, September 1953-August 1954 (pages 361-373).

Arc-Cast Molybdenum Base Alloys, Project N0. 031- 331, First Annual Report, April 1, 1950, by Climax Molybdenum Co. of Michigan, pages 28-30.

DAVID L. RECK, Primary Examiner.

MARCUS U. LYONS, WINSTON A. DOUGLAS,

Examiners. 

1. A CAST ALLOY CHARACTERIZED BY ITS CAPACITY TO BE WORKED AT ELEVATED TEMPERATURES, SAID ALLOY CASTING CONTAINING FROM .005% TO .50% BORON, AT LEAST ONE METAL FROM THE GROUP CONSISTING OF TITANIUM UP TO 14%, ZIRCONIUM UP TO 2%, TANTALUM UP TO 9%, COLUMBIUM UP TO 10%, AND HAFNIUM UP TO 12%, AND THE BALANCE CONSISTING ESSENTIALLY OF METAL FROM THE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN AND MIXTURES THEREOF. 